Many business and science applications use computers to record data, with much of the data being stored on removable media. The removable media may take the form of magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. The advantages of storing data on removable media are numerous. These advantages include a capability of storing large amounts of data (additional cartridges can be used to store additional data), providing a vehicle for long term storage and archival, backing up data which resides on non-removable media, and allowing for easy transfer of data between computers. Removable media typically provides the most economical means of retaining the stored data.
In the past, when a request for a specific removable medium (hereinafter referred to as data cartridge) was made, an operator needed to retrieve the data cartridge and physically load the selected data cartridge into the storage device. This manual mode involved a significant delay while the data cartridge was being retrieved by the operator before the data on that data cartridge could be processed. Additionally, the operator could easily make an error and load an incorrect data cartridge.
With advancements in data storage products, the data cartridges were reduced in size and robots were designed and incorporated to automatically retrieve data cartridges and load those data cartridges into a storage device. The robot is housed within an automated storage library that also contain one or more storage devices and a plurality of data cartridges placed within storage cells. The robot replaced the operator resulting in improved access time and reliability. However, an initial alignment with each of the data cartridges within the storage cells would have to be established to allow for the robot to retrieve a chosen data cartridge. Often a camera is mounted to the robot to provide the feedback for the robot to be aligned with the desired data cartridge. Furthermore, the storage cells would be fixed and accurately located within the automated storage library to improve the reliability of the robot. Removal or shifting of the storage cells (as is possible with magazine type storage cells) requires realigning the robot.
The difficulties and expense that exist with the camera positioning system have been addressed, to some degree, by using a strip encoder to provide positioning feedback. The strip encoder is affixed or aligned to the storage cells and is detected by sensors placed on the picker assembly. Both the strip encoder and the storage cells require identical cell-to-cell spacing (pitch) to accurately locate the picker assembly with each corresponding storage cell. Moreover, the strip encoder needs to be precisely affixed or aligned to the storage cells.
Thus, what is need is a positioning system having a capability to directly detect data cartridges residing in the storage cells. Consequently, the complexity and expense of a camera feedback system is desired to be eliminated; likewise, the location tolerances between a strip encoder and the storage cells could also be eliminated. A positioning system which directly detects the data cartridges should precisely align the picker assembly with the storage cells without requiring the storage cells to be accurately located. Thus the storage cells could easily be removed and replaced within the automated storage library without hindering the alignment method. Furthermore, the data cartridges would not need to be accurately located within the storage cells, which would require less precision when manufacturing the storage cells.